This invention relates to styrene polymer photographic films and a method for making them.
It is known from Canadian Pat. No. 674,921 that photographic films can be prepared from a polystyrene film base if an acrylic copolymer anchoring layer and a gelatin subbing layer are added to the film base before a photographic gelatin emulsion is added. The patent to Starck, U.S. Pat. No. 2,872,318, suggests that the above anchoring layer can be eliminated if a subbing layer is applied from a special mixture of solvents.
Photographic films prepared by these processes are expensive because of the multiplicity of steps involved in their manufacture.
The use of other film bases for photographic purposes has been suggested by U.S. Pat. No. 2,805,173 wherein polyethylene terephthalate is used and U.S. Pat. No. 3,112,199 wherein isotactic polypropylene is used. These patents show that anchoring layers and subbing layers can be eliminated if the polymer surface is treated with a solution of chlorosulfonic acid and then aminated with various amines before a photographic gelatin emulsion is applied. Photographic films prepared by the teachings of U.S. Pat. No. 2,805,173 are expensive due to the high cost of the polymer base. Photographic films prepared by the teachings of U.S. Pat. No. 3,112,199 lack the required stiffness for normal film processing and handling.
When attempts are made to sulfonate polypropylene and polyethylene terephthalate films to a high degree of sulfonation which is necessary for good adhesion, it is found that the film surface turns dark brown or black in the case of polypropylene and crumples away to a powder in the case of polyethylene terephthalate.
In U.S. Pat. No. 3,725,109 a method is claimed for producing a photographic film from biaxially oriented films of styrene polymers by sulfonating them with a sulfur containing compound to produce a film having a high degree of sulfonic acid groups on the surface of the film. It has now been discovered that the quality of photographic film produced according to the process of U.S. Pat. No. 3,725,109 may vary depending on the composition of the photographic gelatin emulsion employed.
A process for sulfonating the surface of polystyrene and exchanging the hydrogen ions in the sulfonated groups with metal ions is disclosed in British Pat. No. 1,100,712.